Supermajor BP has approved a $1.3 billion expansion at its Atlantis field in the US Gulf of Mexico, set to be the third phase for the deep-water stalwart.

BP said on Tuesday that the next stage was enabled by breakthroughs in advanced seismic imaging and reservoir characterisation revealed an additional 400 million barrels of oil in place at the field.

Application of the same technology and analysis used on Atlantis has also identified an additional 1 billion barrels of oil in place at the Thunder Horse field, BP further revealed.